The DNA75 uses 3.7/4.2 volts so you need to parallel the batteries if using more than one. I would suggest that you use batteries that were bought at the same time and haven't used them separately before.When charging the parallel batteries they will charge equally (as one) as long as the internal battery resistances are the same. That's why I suggest buying them at the same time so you get the same lot.The DNA200 and DNA250 use series batteries that require the built in balancer connection.

I've been using 3 paralleled li-pos for a couple of years in my DNA75's.